The present invention is primarily concerned with the field of molding and, more particularly, with the problems encountered with systems which circulate heat-transfer liquids such as hot oils through a mold during the process of molding plastics or other materials in said mold. It is not uncommon for such heating liquids to have a temperature in the area of 450.degree. F., and it has been found that the circulation of such hot liquids has a deleterious effect upon the mechanical circulation pumps through which the liquids must pass. Pumps suitable for use with such liquids are very expensive and have a relatively short life before leakage occurs due to heat-damage of the seals therein. Also, many such pumps are designed to permit the slow leakage of the hot oil for purposes of lubricating the pump. Such leakage is messy and causes a contamination of the atmosphere due to vaporization.
It is also known to circulate cryogenic liquids for cooling or freezing purposes, and to circulate corrosive liquids such as acidic and alkaline liquids through pumps which must be espcially made for such uses and which are expensive and have relatively short lives under the conditions of use.
In many cases a compromise is made with respect to the effectiveness of the work station by moderating the temperature of the circulation liquid. However, this generally results in longer dwell times in the work station, decreased productivity and/or inferior products produced at the work station. It is also known to employ cooling bearings on pumps subjected to elevated temperatures in order to cool said pumps and prevent or retard heat damage thereto. However, such bearings are relatively expensive and require the circulation of coolant therethrough.